Identification of a defect chain motion in n-alkanes by means of nuclear magnetic resonance spin–lattice relaxation time measurements

Proton spin–lattice relaxation time measurements in the rotating frame as a function of inverse temperature have revealed shallow minima not previously observed for a series of n-alkanes ranging from n-C22H46 to n-C41H84. These minima cannot be interpreted in terms of reorientations of methyl groups or entire chains. The most likely reorientational model is one in which a thermally activated trans–gauche defect motion modulates the internuclear dipolar interactions. The results suggest that the gauche defect equilibrium orientation has a higher energy than that of the ordered all-trans equilibrium orientation. Activation energies for the motion as well as energy differences between the two orientations have been extracted from the results for these n-alkanes.